1. Field of the Invention
Embodiments of the present invention relate to the testing of an optoelectronic device and to an optoelectronic device modified for testing. Thereby, the optoelectronic device has the form of a display device with pixels. Particularly, embodiments of the present invention relate to a drive electronics for driving an optoelectronic device, an arrangement of test contact areas and a method for testing an optoelectronic device, especially having the form of a display with pixels.
2. Description of the Related Art
Together with the increasing demand for display elements without a cathode ray tube, the requirements for liquid crystal displays (LCD and other display elements using switching elements like, e.g., thin film transistors (TFT) increase. In these display elements the so-called pixels are arranged in a matrix.
In general, the switching elements of each pixel are driven via control lines, i.e. gate lines, and data lines. In order to avoid charging of the pixel elements, the control lines can be shorted via shorting bars during manufacturing. Otherwise, charging of the pixel elements may result in destruction of the switching elements or the corresponding pixels.
Moreover, developments are underway to—in addition to the pixel elements—apply peripheral drive circuits directly to the glass substrate. Thus, the external driving of the display elements is simplified. Such a display apparatus with integrated drive circuits is described in document DE 198 32 297. In this event, the number of contact areas required for the picture control can be reduced. Without such drive circuits, each control line must have a contactable area to allow for picture control during operation. The areas contactable by an external control are also called pads.
To assure high picture quality, only very few of, e.g., several millions of pixels can be accepted to be defective. To provide low cost production, it is very important, especially for the ever larger display elements, to provide efficient online-testing methods. Such a testing method is disclosed, e.g., in EP 0 523 584. In this testing method, individual pixels are tested by a particle beam. The particle beam can be used to either detect the charge applied via the lines and/or apply charge to a pixel electrode.
Document U.S. Pat. No. 5,081,687 (Henley et al.) describes a method and apparatus for testing LCD displays. Therein, each second data line and each second gate line is connected with a shorting bar. A test picture is generated by driving the shorting bar. During testing, a voltage of, e.g., −5 V is applied to the electrodes of each second pixel and a voltage of, e.g., +5V is applied to the electrodes of the intermediate pixels to form a test picture. Such shorting bars cannot be provided together with integrated drive circuits without troubles because they will short-circuit the driver outputs.
Document U.S. Pat. No. 5,936,687 (Lee et al.) utilizing a drive circuit uses contact pads for generating a test picture, said contact pads being connected with a circuit in order to avoid electrostatic discharge (ESD). This circuit comprises shorting bars which are connected via diodes to the lines for driving the individual pixel elements. In document U.S. Pat. No. 6,337,772 (Ha et al.) transistors are used for connecting the shorting circuits with the control lines.
The following conditions have to be fulfilled if test pictures are generated via the shorting bars connected with a drive circuit. Either the drive circuits are not integrated at the time of the testing or the output terminals of the integrated circuits are formed such that they do not interfere with the test signals. In the majority of cases, this condition cannot be realized.
Furthermore, the following has to be considered. Shorting bars cannot always be realized due to reasons of process, space or circuitry. Also, the function of the drive circuits is not tested with such a solution. Moreover, only simple test patterns can be generated, wherein the periodically repeated unit cell of said test pattern cannot be larger than the number of shorting bars.
If using, for generating a test picture, the pads used during normal operation, especially for large display elements a plurality of contact areas must be contacted during testing. This is especially difficult when large display elements are tested since the display element must be shifted during the testing method. For smaller displays, a plurality thereof is arranged on the glass so that also in this case the glass plate must be repeatedly shifted during the testing procedure. Thus, increased requirements are demanded for the contacting block. The contacting block serves external signal input to the contact areas of the drive circuit or to the contact areas of the data lines or gate lines or the corresponding shorting bars.
Therefore, there is a need for drive apparatus with improved testing properties.